Search

The design of perovskite oxides with improved textural properties in combination with tunable composition variations is a forward-looking strategy for the preparation of next generation catalytic converter. In the present work we report the template-free synthesis of mesoporous solid solutions of La 0.3 Sr 0.7 Ti 1-x Fe x O 3± ? (0

The formation of perovskite oxide nanoparticles supported on ordered mesoporous silica with different pore geometry is here presented. Systematic study was performed varying both pore shape (gyroidal, cylindrical, spherical) and size (7.5, 12, 17nm) of the hosts. LaFeO3, PrFeO3 and LaCoO3 were chosen as target guest structures. The distribution of the oxide nanoparticles on silica was comprehensively assessed using a multi-technique approach. It could be shown that the pore geometry plays a determining role in the conversion of the infiltrated metal nitrates to metal oxide. In particular, slow degradation kinetic was observed in highly curved pores, which fostered nucleation and crystallization of the guest species. In spherical pore systems the enhancement of pore size caused a remarkable delay of the decomposition of the metal salts, but at the same time improved the homogeneous distribution of the oxide particles in the matrix.

This paper reports on the application of a thin MgO interlayer as a diffusion barrier between a Ni 2 MnIn Heusler film and the substrate consisting of either (0 0 1)InAs or a high electron mobility transistor structure with an InAs channel layer. The functionality of the MgO interlayers is studied in dependence of their layer thicknesses. Our studies reveal that MgO interlayers are effective diffusion barriers, which in conjunction with post-growth annealing significantly improve the structural and magnetic properties of the Heusler films. For all as-grown samples, a Curie temperature of 170 K was found indicating that the Ni 2 MnIn films are crystallized in the B2 phase. Post-growth annealing for 15 h at 350 °C of samples with MgO layer thicknesses smaller than 3 nm leads to a strong decrease in magnetisation. This film degradation may be attributed to the intermixing of the Heusler films with substrate material through not-completely closed MgO films. For samples with a MgO interlayer thickness of 3 nm, the Curie temperature increases up to 300 K. This Curie temperature is close to the value reported for bulk Ni 2 MnIn films in the desired L2 1 phase. Furthermore, an increase in saturation magnetisation by a factor of 2.4 was observed.

This paper reports on the influence of deposition temperature on structure and morphology of uncapped Ni 2 MnIn Heusler films grown by molecular beam epitaxy on InAs(0 0 1). Deposition temperatures between 80 and 360 °C and layer thicknesses between 20 and 100 nm have been used. Our studies reveal that during growth beyond 80 °C an intermixing layer arises at the Heusler/substrate interface that is formed by diffusion of arsenic from the substrate. The intermixing process, which is found to take place via interstitial sites, becomes increasingly severe with increasing growth temperature. Furthermore, we find that the films grown at 80 °C are polycrystalline with crystallites in the B2 phase. At 250 °C the films are found to be single-crystalline and pseudomorphically strained in the B2 phase. The desired L2 1 phase and single-crystalline Heusler films are observed at a growth temperature of 300 °C. Interestingly, Heusler films in L2 1 phase are found to have a (1 1 0) surface orientation in contrast to the InAs(0 0 1) substrate crystal. At temperatures higher than 300 °C, strong intermixing and a morphological degradation of the L2 1 Heusler films is observed.

The investigation of ultra-thin self-assembled nanoparticle assemblies is currently receiving an overwhelming interest due to their possible applications in next-generation storage devices. Here, we present a comparative study of the ordering characteristics of monodisperse CoPt 3 arrays deposited on different polymeric surface modifiers employing a spin-coating technique. Using grazing-incidence X-ray scattering, scanning electron microscopy and atomic force microscopy, it is demonstrated that well-ordered nanoparticle films exhibiting correlation lengths in the order of 100 nm may be prepared on bis(3-aminopropyl)-terminated polyethyleneglycol using suitable spin-coating conditions.

CdSe, CdTe and InP nanocrystals were prepared by an organometallic synthesis using mixtures of highly boiling primary amines and trioctylphosphine (TOP) as the coordinating solvent, and were characterized by powder XRD, SAXS, HRTEM, absorption and luminescence spectroscopy. The use of amines allowed us to obtain small crystalline nanoparticles for all materials investigated. In all cases, as-prepared colloids show rather narrow particle size distributions which can be further improved by standard size selective precipitation. Amino-capped II–VI nanocrystals show strong size-dependent band edge photoluminescence (PL). CdSe nanocrystals with the mean particle size in the range of 1.2–3.0 nm exhibit emission from blue to green with room temperature quantum yields of 15–20%. CdTe nanocrystals (2.5–5.0 nm size range) show a PL tunable from green to red with quantum yields up to 65% at room temperature. InP nanocrystals (1.5–4.0 nm size range) possess a weak emission (

Colloidal solutions and redispersible powders of nanocrystalline, lanthanide-doped phosphates and vanadates have been prepared in high-boiling coordinating solvents or by hydrothermal means in aqueous solution. Highly crystalline materials were obtained by both methods despite the low temperature of 200°C applied during the synthesis. The materials have been characterized by using high-resolution TEM, powder-XRD, absorption spectroscopy and luminescence spectroscopy. By analyzing line splitting and intensity pattern in the luminescence spectra of the europium-doped samples, we are able to verify that the dopant ions enter the same lattice sites as in the corresponding bulk material. Size-selected samples of hydrothermally prepared lanthanide-doped YVO4 consist of particles ranging in size from about 10 to 30 nm. The nanoparticles exhibit the tetragonal zircon structure known for bulk material. In the case of LaPO4 the hydrothermal method yields nanoparticles or nano-fibers (width of about 9 nm) depending on the synthesis conditions, while the synthesis in high-boiling solvents yields colloids with a very narrow size distribution and a mean particle size of 4.5 nm. All LaPO4-nanomaterials exhibit the monazite-structure, irrespective of their morphology or size. In all systems investigated, energy transfer between the host and the dopant ions is observed. Upon UV excitation, aqueous colloidal solutions of YVO4:Eu nanoparticles show a luminescence quantum yield of 15% at room-temperature. In LaPO4:Ce, Tb energy transfer is observed between cerium and terbium ions.

Amorphous spherical silica particles with sizes ranging between 100 and 700 nm, depending on the synthetic conditions and post-preparative treatment, self-organize during slow sedimentation into a 3D solid superlattice of artificial opals where uniform silica globules are closely packed in a face-centered cubic lattice. Sintering of the samples increases their rigidity without affecting the 3D regular structure. Artificial opals exhibit a photonic bandgap—an orientation dependent forbidden frequency gap in the visible spectral range. The photonic bandgap feature makes artificial opals promising candidates for optical applications.

Soft X-ray spectroscopy of CdS nanocrystals within their crystalline superlattice allows to relate unambiguously, changes of the electronic structure with the particle size and shape which is known from single crystal X-ray diffraction. We find that the valence and conduction band edge shift contribute to the same extent to the total band gap opening of about 2 eV with respect to CdS bulk as the particle size decreases to 10 A. Taking a finite height of the potential walls into account, we can reproduce these results within an effective mass approximation model.